在 2024/2/4 07:41, Linus Torvalds 写道:
[...]
The thing is, the only reason for the code in
get_mmap_lock_carefully() is for kernel bugs. IOW, some kernel bug
with a wild pointer, and we do not want to deadlock on the mm
semaphore, we want to get back to the fault handler and it should
report an oops.
... and one of the "wild pointers" might in fact be the instruction
pointer, in case we've branched through a NULL function pointer or
similar. IOW, the exception *source* might be the instruction pointer
itself.
Well this is the tricky part of my assumption.
In `exception_epc()` `__isa_exception_epc()` stuff is only called if we
are in delay slot.
It is impossible for a invalid instruction_pointer to be considered as
"in delay slot"
by hardware.
I'd agree that sounds fragile though.
Thanks
So I realy think that MIPS needs to have some kind of "safe kernel
exception pointer" helper. One that is guaranteed not to fault when
evaluating the exception pointer.
Assuming the kernel itself is never built with MIPS16e instructions,
maybe that's a safe assumption thanks to the "get_isa16_mode()" check
of EPC. But all of this makes me nervous.
Linus
--
---
Jiaxun Yang
